This invention relates to a tool clamp mechanism used in a machine tool.
FIG. 1 shows a machine tool employing a conventional tool clamp mechanism disclosed in Japanese Utility Model No. HEI 5-24426. The clamp mechanism includes a hollow spindle 225 which receives a tool 260 at one axial end thereof. The spindle 225 is vertically supported by a spindle head 220. The spindle 225 is rotated by a rotation motor 256 provided to the spindle head 220. The upper end of the spindle 225 is connected to the rotation motor 256 via a coupling 254. A draw bar 265 is slidably provided in the spindle 225. The draw bar 265 is so constituted as to catch the tool 260 when the draw bar 265 is at its upper position, while the draw bar 265 releases the tool 260 when the draw bar 265 is at its lower position.
FIG. 2 is an enlarged view showing a main part of the machine tool of FIG. 1. In order to move the draw bar 265, a swing lever 230 is provided to the spindle head 220. A pin 270 is provided at the top of the draw bar 265, which projects outward through a slot 276 formed on the spindle 225. The swing lever 230 abuts the pin 270 from above. Further, a spring 278 is provided in the spindle 225 for biasing the draw bar 256 upward. With such an arrangement, when the swing lever 230 swings clockwise, the swing lever 230 urges the pin 270 downward. With this, the draw bar 265 is moved downward, so as to release the tool 260. When the swing lever 230 swings counterclockwise, the swing lever 230 releases the pin 270. With this, the draw bar 265 is moved upward (due to the force of the spring 278), so as to catch the tool 260.
In order to miniaturize the machine tool and to reduce the manufacturing cost thereof, it is desired to shorten the whole length of the spindle 225. However, since the swing lever 230 is located above the pin 270, it is necessary to provide a space for the swing lever 230 above the slot 265. Thus, with consideration of limits in shortening the spring 278 and the slot 276, it is difficult to shorten the whole length of the spindle 225. Accordingly, there is a strong demand for a clamp mechanism which enables the shortening of spindle.
Further, the swing lever 230 is generally actuated by a cam member 223 (FIG. 1) located outside the spindle head 220. Thus, one end of the swing lever 230 projects outward from the spindle head 220 through an opening 272 formed on a housing of the spindle head 220. The opening 272 must be large enough to allow the swinging motion of the swing lever 230. With this, cutting chips or cutting oil may enter into the spindle head 220 through the opening 272, which may cause a damage of the spindle 225.
Therefore, there is a strong demand for a clamp mechanism in which the invasion of cutting chips or cutting oil can be prevented.